Electronic devices, such as portable media players, storage devices, tablets, netbooks, laptops, desktops, all-in-one computers, cell, media, and smart phones, televisions and other display devices, navigation systems, and other devices have become ubiquitous in recent years. These devices often include an audio jack through which they receive and/or provide audio information. The audio jacks may include, or be connected to, electronic circuitry such as audio drivers for driving headphones or speakers, audio receivers for receiving audio signals from a microphone, and others. The audio jacks may be arranged to receive audio plugs that may be connected through audio cables to other electronic circuits such as home stereos, powered speakers, headphones or headsets, audio receivers, and other circuits.
These audio plugs may be electrical audio plugs. That is, they may include a number of ring-shaped contacts along their lengths. These contacts may connect to conductors in a cable attached to the audio plug. Contacts for three-pole audio plugs may include left audio, right audio, and ground. Contacts for four-pole audio plugs may include contacts for left audio, right audio, ground, and microphone.
These four-pole audio plug contacts may be configured in a conventional manner. That is, a tip of the audio plug may be a left audio channel contact, followed by a right audio channel, ground, and microphone contacts.
However, some four-pole audio plugs may be configured in an alternate manner. While the tip and following contacts remain a left audio channel contact and a right audio channel contact, the last two contacts are reversed relative to the conventional audio plug. Specifically, the next contact is a microphone contact, followed by ground.
This reversal, as well as the possibility of three or four-pole audio plugs, has necessitated the development of detection circuitry to be included with an audio jack to determine which type of audio plug is inserted. This detection circuit may drive a grounding circuit to ground the appropriate contact in the audio jack. Unfortunately, when power is removed, the grounding circuit may be powered down causing the appropriate contact in the audio jack to no longer be grounded. Under certain circumstances, this may lead to excessive ground noise in another electronic device connected to the audio jack through an audio cable.
Thus, what is needed are circuits, methods, and apparatus for grounding contacts in an audio jack that may avoid this ground noise.